Flexure Strips Research Articles

Microfluidic on-chip valve and pump for applications in immunoassays.

On-chip valves can simplify a microfluidic chip and make it easy to operate. However, most on-chip valves already reported still need complicated manufacture and sophisticated supporting devices. In this work, we present a straightforward on-chip valve, which can be serially connected, to form an on-chip pump. The liquid can horizontally flow one way by the regular deformations of flexure strips in the two valves at both sides of the chamber under pressure changes in microchannels generated by repeated vertical movements of linear actuators. The volume of this system including the chip and the supporting device is 0.65 cubic decimeters, which is much smaller than that of reported systems with a volume of at least 12 cubic decimeters, and the weight of this system is only 0.56 kg, making it possible for point-of-care testing. We carry out an immunoassay of folic acid on chip, and the results show satisfactory reproducibility with acceptable coefficients of variation. We determine 163 clinical human serum samples for folic acid. Furthermore, we detect transferrin, cobalamin and folic acid simultaneously on one chip with both sandwich and competitive binding immunoassay methods. We anticipate that this on-chip valve and pump can be applied in immunoassays and other biosensing applications.

A Compact McKibben Muscle Based Bending Actuator for Close-to-Body Application in Assistive Wearable Robots

In this letter we demonstrate a pneumatic bending actuator for upper-limb assistive wearable robots which uses thin McKibben muscles in combination with a flexure strip. The actuator features both active soft actuation and passive gravity support, and in terms of force transmission bridges the gap between the classic rigid type actuators and the emerging soft actuator technologies. Its flexure strip leverages the high-force low-displacement properties of McKibben muscles towards a large rotational range of motion and reduces localized forces at the attachments. We explain the synthesis method by which these actuators can be obtained and optimized for high specific moment output. Physical specimens of three optimized actuator designs are built and tested on a dedicated experimental setup, verifying the computational models. Furthermore, a proof-of-concept upper-limb assistive wearable robot is presented to illustrate a practical application of this actuator and its potential for close-to-body alignment. We found that based on our currently available components actuators can be built which, given a width of 80 mm, are able to produce a moment exceeding 4 Nm at an arm elevation of 90 deg.

Anelasticity in flexure strips revisited

This note reviews previous analyses by the author of the damping produced by the anelasticity of a simple flexure element that is loaded in tension by an extended object such as a beam balance. The correct calculation of the anelasticity of a simple flexure appeared in an appendix in Quinn et al (1995 Phys. Lett. A 197 197) where the change in the gravitational potential energy due to the shortening of the flexure was calculated enabling expressions for the elastic energy and its associated losses to be derived. Publications prior to this paper did not include this lossless term which led to incorrect predictions of the anelastic losses in flexure pivots in Quinn et al (1992 Phil. Mag. A 65 261–76). In this current paper the derivation of the result is given in such a way that it can be easily contrasted with the expressions in these earlier papers. I also extend the methodology to calculate the elastic and gravitational energy associated with the motion of a suspended object whose dimensions are significantly smaller than the length of the flexure.

An Analytical Formulation for the Lateral Support Stiffness of a Spatial Flexure Strip

A flexure strip has constraint characteristics, such as stiffness properties and error motions, that govern its performance as a basic constituent of flexure mechanisms. This paper presents a new modeling approach for obtaining insight into the deformation and stiffness characteristics of general three-dimensional flexure strips that exhibit bending, shear, and torsion deformation. The approach is based on the use of a discretized version of a finite (i.e., nonlinear) strain spatial beam formulation for extracting analytical expressions that describe deformation and stiffness characteristics of a flexure strip in a parametric format. This particular way of closed-form modeling exploits the inherent finite-element assumptions on interpolation and also lends itself for numeric implementation. As a validating case study, a closed-form parametric expression is derived for the lateral support stiffness of a flexure strip and a parallelogram flexure mechanism. This captures a combined torsion–bending dictated geometrically nonlinear effect that undermines the support bearing stiffness when the mechanism moves in the intended degree of freedom (DoF). The analytical result is verified by simulations and experimental measurements.

Inertial actuator with multiple flexure stacks

An inertial actuator for active vibration control utilizes a single cylindrical actuator module of the “voice coil” type. A moving armature assembly, including a soft iron shell with a tubular sleeve coaxially surrounding a core with two permanent magnets and corresponding pole plates, is suspended compliantly by a flexure assembly including a multiple-stack array of shaped flexure strips and a pair of end support flexure plates mounted to a base. Two magnetically charged annular air gaps at the pole plates in the moving armature traverse two corresponding annular coils wound in a tubular bobbin that extends as a heat-sinking mounting column attached to the base. This form of inertial actuator provides cost benefits along with improved performance and reliability due to the stability of the moving parts and uniformity of linear motion.

Theoretical analysis for the design of the French watt balance experiment force comparator

This paper presents a preliminary analysis for designing a force comparator to be used in the French watt balance experiment. The first stage of this experiment consists in a static equilibrium, by means of a mechanical beam balance, between a gravitational force (a weight of an artefact having a known mass submitted to the acceleration due to the gravity) and a vertical electromagnetic force acting on a coil driven by a current subject to the magnetic induction field provided by a permanent magnet. The principle of the force comparison in the French experiment is explained. The general design configuration of the force balance using flexure strips as pivots is discussed and theoretical calculation results based on realistic assumptions of the static and dynamic behaviors of the balance are presented.

The beam balance as an instrument for very precise weighing

An outline of the principles that should be followed in the design and operation of an equal-arm beam balance for very precise weighing is presented. A detailed discussion on the mechanical aspects of the design and on precautions to be taken to achieve mechanical stability is given. The effects of anelasticity in the pivots, ground vibrations and temperature changes are also described. Comparisons are drawn between the behaviour of knife edges and flexure strips as pivots and between their relative merits. Examples are given of some very precise weighings, reaching in one case a standard deviation of 4 parts in 1012. The factors that may ultimately limit the accuracy of weighing are indicated.

A backlash-free high-precision rotation stage based on flexure strips

A backlash-free high-precision rotation stage based on flexure strips

A 1 kg Mass Comparator Using Flexure-Strip Suspensions: Preliminary Results

This paper describes the design and construction of a novel form of equal-arm balance. The balance has been designed to study the performance of flexure strips for use as pivots in a 1 kg mass comparator working at the highest accuracy. The beam of the balance is servo controlled using optical detection of angular position and electromagnetic control. Small mass differences are measured in terms of the differences in the servo currents required to reproduce the same position of the beam. Preliminary results using this prototype balance indicate that an accuracy in mass comparison of about 5 parts in 1010 can be achieved.

Solid tides recorded with 1 m interval mechanical strainmeter

A TENSIONED-QUARTZ strainmeter 1 m in length has successfully recorded solid tidal strain variations in the Cooney Observatory. The designed is based on the 10-m quartz catenary strainmeter already in use at Cooney1 Vitreosil quartz rods (2-mm diameter) linked with 4-mm diameter Vitreosil hooks comprise the standard. This is tensioned by a brass beam-balance mounted to the hornfels by two 3/8; inch expanding bolts. A single 3/8 inch expanding bolt supports the other end of the quartz standard. Mounted within the fixed body of the beam balance is the coil housing of a Tesa GT10 inductive displacement transducer. The sensor armature is connected to the balance arm, (rotating on flexure strips), entering the transducer coil without contact (see ref. 2 for details).